MediaWiki internal error.

Original exception: [35567c70c6d9cb35fc8d94b7] /index.php?title=C%27t_Billigl%C3%B6sung&action=edit&oldid=5790 Wikimedia\Assert\PostconditionException: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
from /usr/www/users/newtop/wiki/vendor/wikimedia/assert/src/Assert.php(202)
#0 /usr/www/users/newtop/wiki/includes/Title.php(1997): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /usr/www/users/newtop/wiki/includes/skins/Skin.php(549): Title->getRootTitle()
#2 /usr/www/users/newtop/wiki/includes/OutputPage.php(3143): Skin->getPageClasses(Title)
#3 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(395): OutputPage->headElement(SkinMonoBook)
#4 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(129): SkinTemplate->prepareQuickTemplate()
#5 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(146): SkinTemplate->generateHTML()
#6 /usr/www/users/newtop/wiki/includes/OutputPage.php(2634): SkinTemplate->outputPage()
#7 /usr/www/users/newtop/wiki/includes/MediaWiki.php(927): OutputPage->output(boolean)
#8 /usr/www/users/newtop/wiki/includes/MediaWiki.php(940): MediaWiki::{closure}()
#9 /usr/www/users/newtop/wiki/includes/MediaWiki.php(546): MediaWiki->main()
#10 /usr/www/users/newtop/wiki/index.php(53): MediaWiki->run()
#11 /usr/www/users/newtop/wiki/index.php(46): wfIndexMain()
#12 {main}

Exception caught inside exception handler: [35567c70c6d9cb35fc8d94b7] /index.php?title=C%27t_Billigl%C3%B6sung&action=edit&oldid=5790 Wikimedia\Assert\PostconditionException: Postcondition failed: makeTitleSafe() should always return a Title for the text returned by getRootText().
Backtrace:
from /usr/www/users/newtop/wiki/vendor/wikimedia/assert/src/Assert.php(202)
#0 /usr/www/users/newtop/wiki/includes/Title.php(1997): Wikimedia\Assert\Assert::postcondition(boolean, string)
#1 /usr/www/users/newtop/wiki/includes/skins/Skin.php(549): Title->getRootTitle()
#2 /usr/www/users/newtop/wiki/includes/OutputPage.php(3143): Skin->getPageClasses(Title)
#3 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(395): OutputPage->headElement(SkinMonoBook)
#4 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(129): SkinTemplate->prepareQuickTemplate()
#5 /usr/www/users/newtop/wiki/includes/skins/SkinTemplate.php(146): SkinTemplate->generateHTML()
#6 /usr/www/users/newtop/wiki/includes/OutputPage.php(2634): SkinTemplate->outputPage()
#7 /usr/www/users/newtop/wiki/includes/exception/MWExceptionRenderer.php(147): OutputPage->output()
#8 /usr/www/users/newtop/wiki/includes/exception/MWExceptionRenderer.php(66): MWExceptionRenderer::reportHTML(Wikimedia\Assert\PostconditionException)
#9 /usr/www/users/newtop/wiki/includes/exception/MWExceptionHandler.php(106): MWExceptionRenderer::output(Wikimedia\Assert\PostconditionException, integer)
#10 /usr/www/users/newtop/wiki/includes/exception/MWExceptionHandler.php(185): MWExceptionHandler::report(Wikimedia\Assert\PostconditionException)
#11 /usr/www/users/newtop/wiki/includes/MediaWiki.php(565): MWExceptionHandler::handleException(Wikimedia\Assert\PostconditionException, string)
#12 /usr/www/users/newtop/wiki/index.php(53): MediaWiki->run()
#13 /usr/www/users/newtop/wiki/index.php(46): wfIndexMain()
#14 {main}